The present invention relates to a control device for a vehicle equipped with an engine, a motor and a generator.
In recent years, the use of hybrid vehicles equipped with an engine, a motor and a generator is becoming more common due to demand for low pollution, longer travel range and an infrastructure for energy supply. The parallel hybrid vehicle (referred to hereafter as PHEV) which is already in practical use main runs on the engine, and increases fuel cost-performance by assisting the driving force by the motor using the power recovered during deceleration, etc.
On the other hand, there is also a series hybrid vehicle (referred to hereafter as SHEV) which aims at much higher efficiency. In an SHEV, the vehicle is driven only by the motor and the engine is used only for driving a generator. The SHEV as conventionally proposed makes the enhancement of efficiency its primary goal, so the engine is operated under certain fixed conditions for which fuel-cost performance is optimized.
However, in such a SHEV, as it is necessary to vary the running state of a vehicle without changing the driving state of the engine, a battery of sufficient capacity is needed, and an increase of weight and cost cannot be avoided.
The inventors therefore proposed a hybrid vehicle having the same mechanical structure as a SHEV, i.e., an engine, a motor and a generator, wherein the power consumed by the motor for vehicle running is computed at every instant, and the engine and generator are controlled to generate sufficient power for this. If the power consumed by the motor and the power generated by the generator are in agreement, only a minimum capacity is required, the battery which is a factor leading to increased weight and cost can be made compact, and costs can be suppressed. To increase efficiency of the engine in such a vehicle, it is preferable to operate the engine at relatively low rotation speed and high load.
However, if the engine is operated at low rotation speed and high load, as the margin of the engine torque (=maximum engine torquexe2x88x92current engine torque) becomes small, the response of the engine and the generator declines, and a situation may occur wherein the electric power which the motor needs for sudden acceleration of the vehicle, and sharp increase of auxiliary machinery load, cannot be supplied to the motor from the generator.
In such a situation, good operability can be realized without losing acceleration response if the insufficient electric power can be covered by the electric power supplied from the battery. However, if the battery temperature is low, there will be little electric power which can be supplied from the battery, the electric power required for the above-mentioned acceleration will not be forthcoming, and poor acceleration will result.
It is therefore an object of this invention to ensure electric power required for acceleration can be supplied from a battery and ensure good acceleration response when the temperature of the battery is low.
In order to achieve above object, this invention provides a control device for a vehicle, wherein the vehicle comprises an engine, a generator which rotates in synchronism with the engine, and regenerates the output of the engine, a motor driven by the electric power regenerated by the generator, and an electric energy storage device which supplies electric power to the motor, wherein when the electric power supplied to the motor from the generator is insufficient due to response delay of the generation power output from the generator, the electric power to cover the insufficient amount is supplied to the motor from the electric energy storage device, and the control device comprises a sensor which detects the temperature of the electric energy storage device, and a microprocessor programmed to enhance the response of the generation power output of the generator according to the decline of the temperature of the electric energy storage device.
According to an aspect of this invention, a control device for a vehicle is provided, wherein the vehicle comprises an engine, a generator mechanically connected to the engine, a motor electrically connected to the generator, and mechanically connected to the drive shaft of the vehicle, and an electric energy storage device electrically connected to the generator and motor, and the control device comprises a first sensor which detects the running conditions of the vehicle, a second sensor which detects the temperature of the electric energy storage device, and a microprocessor programmed to compute a target motor output based on the running conditions of the vehicle, the target motor output expressing the output of the motor for driving the vehicle according to the running conditions, compute a target engine output based on the target motor output, the target engine output expressing the output of the engine for causing the generator to generate electric power according to the target motor output, compute a first target rotation speed of the generator based on the target engine output, the first target rotation speed expressing the rotation speed of the generator for making the output of the engine coincide with the target engine output at an optimum fuel cost-performance, compute a second target rotation speed of the generator based on the target engine output and the temperature of the electric energy storage device, the second target rotation speed expressing the rotation speed of the generator which makes the output of the engine coincide with the target engine output, and makes the torque margin of the engine a value according to the temperature of the electric energy storage device, select one of the first target rotation speed and second target rotation speed as a third target rotation speed, and control the rotation speed of the generator based on the third target rotation speed.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.